Re: $(<nofile) doesn't set $? to non-zero

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

2018-03-14 14:50:04 +0000, Peter Stephenson:
> On Wed, 14 Mar 2018 14:42:48 +0000
> Stephane Chazelas <stephane.chazelas@xxxxxxxxx> wrote:
> > Would it be worth doing some:
> > 
> >   	ret = readoutput(stream, qt);
> > 	if (errno) {
> > 	  zwarn("%e: %s", errno, s);
> > 	  lastval = cmdoutval = 1;
> > 	}
> > 	return ret;
> > 
> > there (or something cleaner to avoid relying on errno)?
> 
> The return value is the linked list as we're in the context of
> substitution, not command execution, which isn't easy to change without
> a complete rewrite.
[...]

Why not just pass the error as a return argument like in the
patch below?

Then:

$ ./Src/zsh -c 'ERRNO=0; v=$(</x); echo $? $ERRNO $#v'
zsh:1: no such file or directory: /x
1 2 0
$ ./Src/zsh -c 'ERRNO=0; v=$(</); echo $? $ERRNO $#v'
zsh:1: error when reading /: is a directory
1 21 0
$ ./Src/zsh -c 'ERRNO=0; v=$(</dev/mem); echo $? $ERRNO $#v'
zsh:1: permission denied: /dev/mem
1 13 0
$ sudo ./Src/zsh -c 'ERRNO=0; v=$(</dev/mem); echo $? $ERRNO $#v'
zsh:1: error when reading /dev/mem: operation not permitted
1 1 1046296

We still expand to what could be read but signal the error like
when doing the unoptimised $(cat file).


diff --git a/Src/Modules/mapfile.c b/Src/Modules/mapfile.c
index 2503b36..7c5a1e3 100644
--- a/Src/Modules/mapfile.c
+++ b/Src/Modules/mapfile.c
@@ -197,8 +197,9 @@ get_contents(char *fname)
     val = NULL;
     if ((fd = open(fname, O_RDONLY | O_NOCTTY)) >= 0) {
 	LinkList ll;
+	int readerror;
 
-	if ((ll = readoutput(fd, 1)))
+	if ((ll = readoutput(fd, 1, 0)))
 	    val = peekfirst(ll);
     }
 #endif /* USE_MMAP */
diff --git a/Src/exec.c b/Src/exec.c
index e5c6455..32be683 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -4507,6 +4507,8 @@ getoutput(char *cmd, int qt)
     if ((s = simple_redir_name(prog, REDIR_READ))) {
 	/* $(< word) */
 	int stream;
+	LinkList retval;
+	int readerror;
 
 	singsub(&s);
 	if (errflag)
@@ -4514,9 +4516,15 @@ getoutput(char *cmd, int qt)
 	untokenize(s);
 	if ((stream = open(unmeta(s), O_RDONLY | O_NOCTTY)) == -1) {
 	    zwarn("%e: %s", errno, s);
+	    lastval = cmdoutval = 1;
 	    return newlinklist();
 	}
-	return readoutput(stream, qt);
+	retval = readoutput(stream, qt, &readerror);
+	if (readerror) {
+	  zwarn("error when reading %s: %e", s, readerror);
+	  lastval = cmdoutval = 1;
+	}
+	return retval;
     }
     if (mpipe(pipes) < 0) {
 	errflag |= ERRFLAG_ERROR;
@@ -4537,7 +4545,7 @@ getoutput(char *cmd, int qt)
 	LinkList retval;
 
 	zclose(pipes[1]);
-	retval = readoutput(pipes[0], qt);
+	retval = readoutput(pipes[0], qt, 0);
 	fdtable[pipes[0]] = FDT_UNUSED;
 	waitforpid(pid, 0);		/* unblocks */
 	lastval = cmdoutval;
@@ -4562,7 +4570,7 @@ getoutput(char *cmd, int qt)
 
 /**/
 mod_export LinkList
-readoutput(int in, int qt)
+readoutput(int in, int qt, int *readerror)
 {
     LinkList ret;
     char *buf, *ptr;
@@ -4591,6 +4599,8 @@ readoutput(int in, int qt)
 	}
 	*ptr++ = c;
     }
+    if (readerror && ferror(fin))
+	*readerror = errno;
     fclose(fin);
     while (cnt && ptr[-1] == '\n')
 	ptr--, cnt--;